The present invention relates to a new masking member used to protect the inside and circumference of a hole such as a water outlet hole, a cable piercing hole, and the like from a surface treatment such as coating, plating, phosphatizing, vacuum evaportion and the like. More particularly, the present invention relates to a new masking member consisting of an inserting part and a double flange formed at the base of said inserting part wherein the diameter of the outer part of said double flange is larger than the diameter of the inner part of said double flange. In a case where a surface treatment is effected on the surface of an article, said surface of said article often has hole(s) whose inside must be protected from said surface treatment. Said hole(s) may be a water outlet hole, a cable piercing hole, and the like, and a grummet, a plug, a bolt and the like may be inserted into said hole(s).